1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus for supplying a video signal to a display unit.
2. Description of the Related Art
A monitoring system or the like which uses a plurality of TV cameras is so designed as to enable the simultaneous reproduction of video signals of the respective TV cameras. When such a plurality of reproduced pictures are displayed, a method of displaying the images picked up by the respective TV cameras on the corresponding TV monitors, a method of displaying the plurality of pictures on one TV monitor by time sharing, or a method of displaying the pictures by dividing the screen of the TV monitor into the corresponding number of regions is adopted. In a general monitoring system, only the reproduction of a plurality of pictures is required and since a high resolution is not particularly necessary in most cases, there is a tendency to adopt a method of displaying a plurality of reproduced pictures on one TV monitor with the reproducing screen divided into the corresponding number of regions.
FIG. 1 is a block diagram of the structure of an image pickup system for displaying a plurality of reproduced pictures on one TV monitor. In FIG. 1, four TV cameras 1 to 4 are used for displaying four reproduced pictures on one TV monitor 5.
Each of the TV cameras 1 to 4 is connected in parallel to a main controller 6 and video signals Y.sub.1 to Y.sub.4 which are output from the respective TV cameras 1 to 4 are input to the main controller 6. The main controller 6 is provided with a synchronizing signal generator 6a, a screen controller 6b and a field memory 6c, and not only synchronizes the operation of each of the TV cameras 1 to 4 at a predetermined timing but also compounds the video signals Y.sub.1 to Y.sub.4 into a composite video signal Y.sub.m for simultaneously displaying the four images on the same screen, and supplies the composite video signal Y.sub.m to the TV monitor 5.
The synchronizing signal generator 6a supplies a synchronizing signal SY to each of the TV cameras 1 to 4 so as to make TV cameras 1 to 4 have the same operation timing. The screen controller 6b reduces the video signals Y.sub.1 to Y.sub.4 obtained from the TV cameras 1 to 4, respectively, to 1/2 both in the horizontal scanning period and in the vertical scanning period, temporarily stores the picture information which corresponds to the four pictures in the field memory 6c and reads out the image information from the field memory 6c in a predetermined order so as to generate the composite video signal Y.sub.m. To be more precise, the video signals Y.sub.1 to Y.sub.4 are stored in the field memory 6c with the data thereof culled out on every other pixel both in the horizontal scanning period and in the vertical scanning period, and the image information which corresponds to the images from the TV cameras 1 to 4 is read out in every 1/2 horizontal scanning period and every 1/2 vertical scanning period to generate the composite video signal Y.sub.m.
For example, in the case of displaying pictures on the four divided regions A to D, as shown in FIG. 2, in the former 1/2 vertical scanning period, the picture information which corresponds to the video signal Y.sub.1 is read out in the former 1/2 horizontal scanning period and the image information which corresponds to the video signal Y.sub.2 is read out in the latter 1/2 horizontal scanning period. In the latter 1/2 vertical scanning period, the image information which corresponds to the video signal Y.sub.3 is read out in the former 1/2 horizontal scanning period and the picture information which corresponds to the video signal Y.sub.4 is read out in the latter 1/2 horizontal scanning period. In this way, the images picked up by the TV cameras 1 to 4 are simultaneously displayed in the divided regions A to D, respectively, of the reproducing screen.
In the above-described image pickup system, the main controller 6 is inevitable for not only controlling the operations of the plurality of TV cameras 1 to 4 but also generating the composite video signal Y.sub.m for producing the four divided reproduced pictures from the video signals Y.sub.1 to Y.sub.4. Such a main controller 6 requires a large-scale circuit structure such as the field memory 6c for storing the image information for at least four pictures and the screen controller 6b for reading out the image information from the field memory 6c and compounding it. A plurality of circuits for connecting the TV cameras are also necessary. Thus, this kind of image pickup system suffers from a high cost.
In addition, since the video signals Y.sub.1 to Y.sub.4 obtained from the TV cameras 1 to 4 are culled in the horizontal and vertical directions and compacted, the resolution intrinsic to each of the TV cameras 1 to 4 is not made the most of and the system involves much waste.